In mammals, sperms are exposed to a microenvironment created by the absorptive and secretory activities of the epididymal epithelium cells (Cooper, 1998). Passing along the epididymal duct, sperm undergo morphological and functional modifications (Jones, 1998), which culminate in the acquisition of forward motility and the ability to recognize and penetrate the zona pellucida of egg (Cooper, 1990; Liu et. al., 1991; Turner, 1995). Epididymal secretions contain many kinds of proteins including superoxide dismutase (Perry et. al., 1993), peroxidase (Ghyselinck, et. al., 1993), glycosidases (Toshimori et. al., 1988) transport proteins, as well as sperm maturation antigens (Araki et. al., 1992; Mahony et. al., 1994; Weaver et. al., 1993). It is believed that interaction between epididymal secretary proteins and sperm membrane during sperm maturation is required for normal fertility in the male (Myles, 1993). However, the roles of epididymal secretary proteins in sperm maturation are not well defined (Myles, 1993; Cornwall and Hann, 1995).
A novel family of transmembrane proteins that contain a disintegrin and metalloprotease (ADAM) domain had been identified in a variety of tissues and species (Primakoff and Myles, 2000). Total of 29 ADAM cDNAs have been cloned and sequenced (Stone et al., 1999; Primakoff and Myles, 2000). Although the biological functions are not well defined, ADAMs are found involved in rather diverse biological processes, such as virus-cell fusion (Hermandeez et al, 1996), neurogenesis (Schlondorff and Blobel, 1999) and fertilization (Blobel et al, 1992; Bigler et al, 1997). A full-length ADAM cDNA encodes a multi-domain protein containing pro-domain, metalloprotease, disintegrin, cysteine-rich, epidermal growth factor (EGF)-like, transmembrane, and cytoplasmic domains (Wolfsberg et al., 1995 a, b; Primakoff and Myles, 2000). Among the 29 known ADAM cDNAs, 12 are testis-specific and 3 are testis-predominant (Primakoff and Myles, 2000). These 15 ADAMs are proposed to play important roles in spermatogenesis or/and fertilization. The inhibition of sperm-egg fusion by fertilin □ (ADAM2)-specific monoclonal antibody (Primakoff et al, 1987) further substantiates the role of ADAM in fertilization. The ADAM7 molecules found in the rat, monkey (Perry et al, 1992) and mouse (Cornwall and Hsia, 1997) are all epididymis-specific and proposed to be involved in sperm maturation. However, biological functions of ADAMs in sperm maturation and fertilization are not yet defined.